[backup] Add integration and performance tests

Summary:
ENG-4511
Add tests for backup. They are not deterministic yet (they require a clean cloud), I'm going to update them as a followup if I have the time.

Depends on D8965

Test Plan: Run both integration and performance tests

Reviewers: bartek, patryk, kamil, jon

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8966